This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2001-358062, filed on Nov. 22, 2001; the entire contents of which are incorporated herein by reference.
This invention relates to a nano-imprinting method, magnetic printing method and recording medium. More particularly, the invention relates to a nano-imprinting method or a magnetic printing method including a novel technique for imprinting a physically embossed micro pattern or a magnetic micro pattern on a substrate surface by tightly pressing a master plate to the substrate surface, and a recording medium made by the method.
Epoch-making enhancement of functions of information devices such as personal computers has brought about a significant increase of the information volume dealt with by users. Under the circumstance, anticipation for information record/reproduce devices with much higher recording densities and semiconductor devices with much higher degrees of integration than now is getting greater and greater.
In order to enhance the recording density, more enhanced micro fabrication techniques are required. Conventional photolithography using an exposure process enables micro fabrication of a large area simultaneously. However, since the technique does not have the resolving power below wavelengths of light, it is difficult to make a microstructure as minute as 100 nm or less, for example, with this technique. As conventional fabrication techniques in the level as minute as 100 nm or less, there are electron beam lithography and focused ion beam lithography among others. A problem with these techniques is a bad throughput.
There is a technique for fabricating a microstructure more minute than wavelengths of light with a high throughput, which is the xe2x80x9cnano-imprinting lithography (NIL) techniquexe2x80x9d proposed in Appl. Phys. Lett.; Vol. 77 (1995) p.3114 in 1995 by S. Y. Chou et al. The nano-imprinting lithography is a technique that prepares a master plate having formed a predetermined embossed micro pattern beforehand by electron beam lithography, for example, and transfers the embossed pattern of the master plate to a resist film of a substrate by pressing the master plate to the substrate coated with the resist. This technique takes much shorter time than electron beam lithography and focused ion beam lithography for one cycle of fabrication per area of one square inch or more.
The existing nano-imprinting process has the following steps.
(1) A resist film of PMMA or the like is coated on a silicon substrate.
(2) The master plate is pressed against the substrate in an atmosphere of a reduced pressure. The pressure is approximately 100 bars.
(3) The substrate coated with the resist is heated to a temperature not lower than the glass transition temperature of the resist.
(4) After a certain duration of time, the master plate and the substrate are cooled to the room temperature.
(5) The master plate is separated from the substrate.
(6) The substrate is obtained with the embossed pattern on the resist.
In the above steps, the step of heating the substrate to the glass transition temperature or higher is necessary for softening the resist and enabling transfer of the embossed pattern even with a low pressure. However, since this step rakes time for heating the substrate and additionally requires the time for the next cooling step, the heating step is a factor of degradation of the throughput.
In case the imprinting is carried out in a heated atmosphere not lower than the glass transition temperature of the resist, since the resist softens, local xe2x80x9cexfoliation of the resist filmxe2x80x9d may occur in the step of separating the master plate from the resist substrate after the imprinting step due to partial cohesion of the resist on the part of the master plate separated away.
The step of the imprinting is carried out in a reduced-pressure atmosphere to prevent local failure of the transfer due to existence of bubbles between the master plate and the resist substrate surface. However, to make the reduced pressure atmosphere for the imprinting, it takes time for degassing by a pump or the like, and this step is another factor of degrading the throughput.
In order to transfer the embossed pattern of the master plate uniformly to the wide area not smaller than one square inch, highly parallel alignment of the master plate surface and the substrate surface is required. Additionally, it is very difficult to uniformly apply the weight over the wide area.
As discussed above, although the nano-imprinting technique is suitable for fabrication of a microstructure as minute as wavelengths of light, and makes it possible to fabricate a microstructure with much higher throughput than electron beam lithography and the lithographic process by focused ion beams, the time required for heating and cooling the substrate adversely affects the throughput, and this technique involves the problems of exfoliation of the film, local failure of transfer of the embossed pattern due to bubbles, difficulty of parallel alignment of the substrate surface and the master plate surface, and difficulty of uniform weighting.
According to an embodiment of the invention, there is provided a nano-imprinting method for transferring an embossed pattern from a master plate having the embossed pattern to a pattern-receiving surface of a pattern-receiving element, comprising: preparing the master plate having an information carrier region on which the embossed pattern is formed, and a substantially flat information-free region; preparing the pattern-receiving clement having the pattern-receiving surface which has a size corresponding to the information carrier region plus at least a part of the information-free region; preparing a buffer layer which is smaller than the master plate and the pattern-receiving surface and has a shape corresponding to the information carrier region; and applying a pressure to the master plate and the pattern-receiving clement by a pair of press surfaces holding the master plate, the pattern-receiving element and the buffer layer.
According to another embodiment of the invention, there is provided a nano-imprinting method for transferring an embossed pattern from a master plate having the embossed pattern to a pattern-receiving surface of a pattern-receiving element in form of a substantially cylindrical drum having the pattern-receiving surface on a side surface thereof, comprising: preparing the master plate having an information carrier region on which the embossed pattern is formed, and a substantially flat information-free region; preparing the pattern-receiving element having the pattern-receiving surface which has a size corresponding to the information carrier region plus at least a part of the information-free region; preparing a buffer layer which is smaller than the master plate and the pattern-receiving surface and has a shape corresponding to the information carrier region; and pressing and rolling the pattern-receiving element over the master plate placed on a press surface via the buffer layer.
According to yet another embodiment of the invention, there is provided a magnetic printing method for transferring a magnetization state of a magnetized embossed pattern from a master plate having the embossed pattern to a magnetic layer of a magnetization-receiving medium, comprising: preparing the master plate having an information carrier region on which the embossed pattern is formed, and a substantially flat information-free region; preparing the magnetization-receiving medium having a magnetization-receiving surface of the magnetic layer, the magnetization-receiving surface having a size corresponding to the information carrier region plus at least a part of the information-free region; preparing a buffer layer which is smaller than the master plate and the magnetization-receiving surface and has a shape corresponding to the information carrier region; and applying a pressure to the master plate and the magnetization-receiving medium by a pair of press surfaces holding the master plate, magnetization-receiving medium and the buffer layer.
According to yet another embodiment of the invention, there is provided a magnetic printing method for transferring a magnetization state of a magnetized embossed pattern from a master plate having the embossed pattern to a magnetic layer of a magnetization-receiving medium in form of a substantially cylindrical drum having the magnetic layer on a side surface thereof, comprising: preparing the master plate including an information carrier region on which the embossed pattern is formed, and a substantially flat information-free region; preparing the magnetization-receiving medium having a magnetization-receiving surface of the magnetic layer, the magnetization-receiving medium having a size corresponding to the information carrier region plus at least a part of the information-free region; preparing a buffer layer which is smaller than the master plate and the magnetization-receiving surface and has a shape corresponding to the information carrier region; and pressing and rolling the magnetization-receiving medium over the master plate placed on a press surface via the buffer layer.
According to yet another embodiment of the invention, there is provided a recording medium having a data region in which a patterned recording layer is formed, and capable of rotating about a rotation axis to enable at least reproduction or recording of data, characterized in having a positioning pattern in a region within 300 xcexcm adjacent to the data region to be referred to upon reproduction or recording.
These embodiments of the invention make it possible to fabricate a microstructure as minute as 200 nm or less on a large-area region not smaller than one square inch with a high throughput by using the nano-imprinting technique. That is, the embodiments enable fabrication of a high-density recording medium with a high throughput, and are therefore greatly advantageous in the industry